Influence of Modifying Mixtures on Si Crystal Formation in Al-7%Si Alloy

Abstract

Using scanning and transmission electron microscopy, we studied silicon particles formed during the solidification of Al-7%Si alloy when different modifying mixtures were introduced into the melt: (1) a mixture of ultrafine powders Na 3 AlF 6 + K 2 ZrF 6 + TiO 2 + ZrO 2 ; (2) K 2 ZrF 6 ; and (3) the flux Arsal. By differential scanning calorimetry, it was established that modifying mixtures significantly influenced the temperature of the solidification processes. The formation of two types of Si crystals was established. The first type of Si crystals precipitated during the solidification of the eutectic mixture (α-Al + Si) in the form of needles or plates. The second type of Si crystals was segregated from eutectic Al-phases or segregated from the solid phase α-Al upon cooling in the solid state. The introduction of modifiers led to a shift in solidification temperatures. When fluoride salts were used, there was an increase in the temperature of eutectic solidification. Silicon crystals were large (up to 10 µm), with a local excess of aluminum concentration.

Preparation Method of Spherical and Monocrystalline Aluminum Powder

“…In the cooling curve, a low-energy exothermic peak (VII) that follows the aluminum solidification peak is observed ( Figure 1f). This peak is attributed to solidification of an Al-Si near-eutectic phase [17].…”

“…Table 1 presents the specific temperatures of registered reactions. Solidification of Al-Si based particles [17] followed by solidification of Al-AlFeSi-Si ternary eutectics [19] As presented in Table 1, the higher temperature of the heat treatment (1423 K) visibly shifted the solidification temperature of the aluminum particles to lower temperatures when compared to the sample C heat treated at 1023 K. A similar finding, but exhibiting lower shift values, was also reported by Yang et al [18]. The early nucleation was attributed to the presence of Al 2 O 3 which acted as nucleation sites during solidification.…”

On the Role of Hazard and Particle Failure Statistics on the Variation of Fracture Parameters of Ductile-Brittle Composites

“…To obtain spherical silicon particles, the samples were maintained at 560 • C for 10 days and quenched in water. Compared to a shorter one-day long treatment in [9], the resulting material showed a good reproducibility of mechanical properties, in particular, a high enough maximum elongation corresponding to fracture strain ε > 10%, thus indicating stabilized α-Al matrix conditions [22,49]. Optical and electron microscopy were applied to evaluate the particles spheroidization.…”

Rheo-Squeeze Casting of High-Silicon Aluminium Alloy Pipes with Gradient Structures and Their Mechanical Properties

“…Al-Si alloys have good casting properties, stable hightemperature performance, and its casting has good air-tightness [1][2] . Using Al-Si alloys to make fuel engines has become the trend in automobile manufacturing industry since the 1970s 3 .…”